Some companies like_Avid,_Hayes, Shimano_XT only use 74mm post mount calipers with adapters for use with International Standard (IS) frames and forks. For these, no adapter is required for Manitou_forks. In fact, you take the adapter off to use with_Manitou. Other companies like Magura, Hope_and Shimano_XTR have 74mm calipers are available as an option so again no adapter would be required.

The only time you must use an adapter is if you buy brakes with a fixed IS caliper. Then you would need to get the IS to post mount adapter. This adpater requires a 20mm larger rotor than the caliper was originally designed for. This typically only happens when you already have the brakes and switch forks from IS to Manitou_post mount.

If you happen to need the IS to PM adapter, I have one leftover from when I first switched to_Manitou. I've since upgraded the brakes with a PM caliper type and sold the IS brakes.